Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (Details) number in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Total Annual remediation expense and interest	$ 10,000
Financial Derivative, Nonmonetary Notional Amount	317,100	229,925	346,875
Derivative, Nonmonetary Notional Amount	169,978	250,250	404,645
Notional Amount of Foreign Currency Derivatives	$ 6,852	$ 8,690	$ 9,025
Operating revenues	255,529	261,665
Derivative, Loss on Derivative	15,500	14,100
Unrealized loss On Derivatives	17,200
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1,800	600	2,700
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	17,900	24,200	25,500
Derivative Fair Value Of Derivative Net	16,100	23,600	$ 22,800
Natural Gas Commodity [Member]
Derivative [Line Items]
Cost of sales	(16,379)	(23,481)
Operating revenues	0	638
Less:Amounts deferred to regulatory accounts on balance sheet	16,379	23,065
Total Impact On Earnings	0	222
Foreign Currency [Member]
Derivative [Line Items]
Cost of sales	241	(741)
Operating revenues	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	(241)	741
Total Impact On Earnings	$ 0	$ 0